Luciferases are defined by their ability to produce luminescence. Beetle luciferases form a distinct class with unique evolutionary origins and chemical mechanisms (Wood, 1995).
Although the enzymes known as beetle luciferases are widely recognized for their use in highly sensitive luminescent assays, their general utility has been limited due to low thermostability. Beetle luciferases having amino acid sequences encoded by cDNA sequences cloned from luminous beetles are not stable even at moderate temperatures. For example, even the most stable of the luciferases, LucPpe2, obtained from a firefly has very little stability at the moderate temperature of 37° C. Firefly luciferases are a sub-group of the beetle luciferases. Historically, the term “firefly luciferase” referred to the enzyme LucPpy from a single species Photinus pyralis (Luc+ is a mutant version of LucPpy, see U.S. Pat. No. 5,670,356).
Attempts have been reported to mutate natural cDNA sequences encoding luciferase and to select mutants for improved thermostability (White et al., 1994; from P. pyralis, and Kajiyama and Nekano, 1993; from Luciola lateralis.) However, there is still a need to improve the characteristics and versatility of this important class of enzymes.